One of the primary components in paint is the "film former" that provides a film for the protective function of a substrate coated with paint. Film forming components of liquid paints include resins which have required organic solvents to provide the resins with suitable viscosities such that the paint can be applied by existing commercial application equipment. Use of solvents, however, raises at least two problems. First, in the past and potentially in the future, petrochemical shortages mitigate against the use of organic solvent in great volumes. Second, environmental concern mitigates against the use of organic solvents and requires such use be minimized.
Thermosetting coating compositions, particularly coating compositions which include polyester, alkyd, acrylic and epoxy polymers are often materials of choice for making film formers for various substrates to which the coating composition is applied. Coating compositions provide a protective function for the substrate. Hence, coating compositions are generally formulated to provide a balance of properties which will maximize hardness, flexibility, solvent resistance, corrosion resistance, weatherability, acid resistance, hydrolytic stability and gloss with an emphasis on certain properties depending upon the purpose for which the coating is intended.
It has been a continuing challenge to provide coating compositions which upon thermosetting provide films with desired film properties such as hardness, flexibility, solvent resistance, corrosion resistance, weatherability, acid resistance, hydrolytic stability and gloss, reduce VOCs and still retain the ability to have the viscosities of the polymeric vehicle and formulated coating composition made therefrom such that the formulated coating composition can be applied with existing commercial application equipment.
U.S. Pat. No. 4,331,782 to Linden, U.S. Pat. Nos. 3,836,491 and 3,789,044 to Taft et al. and U.S. Pat. No. 3,409,579 to Robbins describe phenol capped polymers which are crosslinked with polyisocyanates. They do not involve the use of a phenolic urethane reactive diluent which is cross linked or the use of such a diluent in a system which includes a polyol, diluent and crosslinking agent.